1. Field of the Invention
The present invention relates to a tissue sealant. More particularly, the present invention relates to a tissue sealant which can seal injuries, reduce loss of blood, maintain a hemostasis, and promote healing of an injured site on a skin surface, organs or the like.
2. Description of the Related Art
Shortly after injuries occur, a healing of injuries, i.e., a recovery of lesions, starts with an adhesion and agglutination of platelets or thrombocytes to the injuries. It is necessary to closely control the consecutively conjugated functions of various cells, and the degradating and regenerating processes. These include a formation of fibrin clots, absorption of blood clots, and epithelialization. The injury-healing comprises a formation of many blood capillaries, active fibroblasts, and collagen fibrils, but is not followed by a formation of a particular skin structure.
A process of healing injuries starts with an adhesion and agglutination of platelets to an injured tissue, and with thromboplastin liberated from the injured cells at the same time. Thromboplastin activates coagulation factors, and finally converts prothrombin to thrombin. By a catalyzing action of thrombin, fibrinopeptides A and B are released from fibrinogen to form fibrin monomers. The monomers are aggregated to form fibrin filaments. Thrombin also activates the blood coagulation factor XIII (the Factor XIII), which catalyzes an isopeptide formation to covalently cross-link fibrin filaments. Then, .alpha.-antiplasmin is bonded to fibrin filaments by the activated Factor XIII, whereby a degradation of fibrin filaments by plasma components is prevented.
The platelets adhered and agglutinated to the injured site liberate PDGF's. PDGF's include a platelet-derived growth factor (PDGF), a platelet-derived angiogenic factor (PDAF), a transforming growth factor-.beta. (TGF-.beta.) and a platelet factor-4 (PF-4).
PDGF is a mitogen, and stimulates a protein synthesis in cells originating in mesenchyme, such as fibroblastes and smooth muscle cells. PDGF is an amitosis attractant for an endothelial cell.
TGF-.beta. is an attractant for a macrophage and monocytes. TGF-.beta. stimulates or inhibits various cells, dependent upon the presence or absence of other growth factors. For example, when applied in vivo, TGF-.beta. increases a tension-strength of a cured skin of an injury. Further, TGF-.beta. stimulates a synthesis of collagen and glucosamine glycan.
A growth factor liberated from the platelet is potentially useful in specifically promoting a healing of injuries and a recovery of tissues. It was experimentally proved that a closure of injuries, growth of blood vessels or the like is facilitated by applying an extrinsic growth factor to an injured site. Therefore, the safest method for a living body is to utilize growth factors liberated from the platelets adhered and agglutinated onto an injured site.
As a composition for sealing an injured site, reducing a loss of blood, and maintaining a hemostasis, a surgical adhesive and tissue sealant containing plasma proteins are known, and used in the sealing of injured sites on a skin surface or intracorporeal organ. Such a sealant generally contains one or more blood coagulation factors and other plasma proteins. For example, European Patent No. 0,068,047 discloses an anhydrous powder material derived from a concentrated plasma fraction containing fibrinogen, fibrinolysis inhibitors, and thrombin or prothrombin. However, the material can be applied only in the form of powder, because blood clots are formed immediately after water is added. Further, AU-A75097/87 discloses a one-component adhesive containing fibrinogen, the Factor XIII, a thrombin inhibitor such as antithrombin III, a prothrombin factor, a calcium ion, and optionally, a plasmin inhibitor. U.S. Pat. Nos. 4,427,650 and 4,427,651 disclose an enriched plasma derivative containing fibrinogen, thrombin and/or plasmin, and fibrinolysis inhibitors, and optionally, other components such as platelet extracts. U.S. Pat. Nos. 4,627,879 and 4,928,603 disclose a cryoprecipitated suspension containing fibrinogen and the Factor XIII, and a use thereof in the preparation of a fibrin glue, or a fibrin adhesive.
The fibrin adhesive is called a fibrin sealant, and was initially formulated for a clinically topical application, and used for controlling bleeding and curing injuries. The fibrin adhesive is prepared from plasma, and an exact composition of a particular fibrin adhesive depends on a particular plasma fraction used as a starting material. Generally, the fibrin adhesive contains a mixture of proteins which can form blood clots when admixed with thrombin. For example, the fibrin adhesive may be prepared by cryoprecipitating plasma, and fractioning the precipitate to obtain a composition which can form a sealant or blood clots when admixed with thrombin or a thrombin activator. The fractionating of plasma components can be carried out by standard methods of purifying proteins, for example, a precipitation with ethanol, polyethylene glycol or ammonium sulfate, an ion-exchange, or a gel filtration chromatography. In general, the fibrin adhesive comprises a fibrinogen concentrate containing fibronectin, the Factor XIII, and the von Willebrand factor, and dried human or bovine thrombin. It is prepared as a lyophilized form, and admixed with calcium chloride shortly before use. After the admixing, the components are aggregated on the tissue surface to form blood clots containing cross-linked fibrins. The Factor XIII is contained in the fibrinogen concentrate, and catalyzes the cross-linking reaction. The fibrin adhesive seals the surfaces of tissues, and prevents air or liquid from leaking, to thereby induce a hemostasis. The fibrin adhesive promotes the healing of an injury by means of functions to stop bleeding and prevent a flow of blood from an injury.
However, such a conventional fibrin adhesive per se does not exhibit a property of curing or healing an injury. Therefore, it is desired to develop a fibrin adhesive which can be applied to an injury on a skin surface or an intracorporeal tissue, and is useful to maintain a hemostasis and enhance a property of curing or healing an injury.